Can I have clarification as to where all the earthing points are please?

Is the one for the rail/intake, on the engine hook that bolts to the head or is there another one somewhere?

I would like to point out that I am using a 4AGE head, as a cam cap bolt sheared off inside my GZE head. The bolt was drilled out but on the wonk, so instead of elongating the cam cap hole, I swapped heads over with my spare GE head.

I had a spare 45 mins earlier tonight to take the rail off and get inside that part of the loom...

I traced back injector 1 ground wire to where it splits off from another ground. Where the injector 1 ground splits off the main ground wire, the rest of that wire looks like it goes towards the dizzy end. Too dark and not enough time to trace back where that goes to. Going by the wiring diagram it should only ground injectors 1&2?

Where the injector 1 ground is connected spliced into the other wire it's not great but testing it, it shows between 0 and 0.4 volts. Doing the same test on the other injectors all the grounds show 0v as they should. I'm going to have to trace this main wire back aren't I?

It is usual for all the injector wires (power and ground) to run within the engine loom until they separate with the power wires going to the resistor pack and the ground wires continuing on to the ECU. I've never had an AW11 but judging by Corollas of similar vintage, all the 2 > 1 splices will be in the loom not that far from the injectors.

Usually one wire is continuous and the other is connected to it with a brass crimp. The join is then covered with some tough tape applied longitudinally. Perhaps the tape has been removed for the splice pictured ?

An ECU ground is not the same thing as a engine ground. The ECU grounds are three or four usually brown wires that exit the engine loom close to the injectors and bolt down with one of the bolts that hold the engine loom on the intake side of the engine.

There is also one heavy black ground wire from the engine to the chassis and this is usually located close to the starter motor.

Cheers... jondee86

The reasonable man adapts himself to the world; the unreasonable onepersists in trying to adapt the world to himself. Therefore, all progressdepends on the unreasonable man.

Since you have the red-black wire striped back to the tee connection, Use a VOM [preferred] or continuity lite with a long test lead and verify that the red wire with the black trace, that runs to the ECU plug is good. There could be a break or enough resistance to screw up the engine ECU. You may want to put a drop of solider on these wire connections. Also verify the continuity of the ground wires for all the injectors running out of the ECU. Davew7

Here is a pic of how the factory insulates a two into one splice with several turns of black tape. When the splice is unwrapped it should look like the lower image. The factory uses an uninsulated butt crimp that is not easy to find in shops. So if your crimp looks like the one in the pic it is probably a factory crimp.

The injector ground wires should all head in the same direction (towards the ECU) and get bundled up with sensor wires and most likely with the timing signal wires from the distributor. The engine loom will get thicker as it heads towards the ECU and picks up more sensor wires along the way.

The injector ground wires connect to transistors inside the ECU. The ECU switches the transistor ON (briefly) to connect the injector ground to the chassis ground and allow current to flow through the injector causing it to fire. Because the injector ground wire is not directly connected to chassis ground, if the battery is connected it is possible for the injector ground to be floating at a potential a few millivolts above chassis ground.

This is not a problem. If the battery is disconnected the reading will go to zero.

Cheers... jondee86

The reasonable man adapts himself to the world; the unreasonable onepersists in trying to adapt the world to himself. Therefore, all progressdepends on the unreasonable man.

The odds are low, but the problem could actually be the crimp in jondee86's photo or pin/plug connectors. I had increase resistance at a brass crimp where several sensor wires tee'd into a common ground wire. That is why I commented on solidering these 30 year wire joints. You have to check every wire and connection in the injector circuit. To rule out an open or high resistance in the circuit. If the wires are OK, then it time to swap out the ECU. Davew7

davew7 wrote:The odds are low, but the problem could actually be the crimp in jondee86's photo or pin/plug connectors. I had increase resistance at a brass crimp where several sensor wires tee'd into a common ground wire. That is why I commented on solidering these 30 year wire joints. You have to check every wire and connection in the injector circuit. To rule out an open or high resistance in the circuit. If the wires are OK, then it time to swap out the ECU. Davew7

To rule out high resistant, measure it with a multimeter. Soldering has its applications but it's not ideal for this. If there is a problem, crimp them back together.

jondee86 wrote:Here is a pic of how the factory insulates a two into one splice with several turns of black tape. When the splice is unwrapped it should look like the lower image. The factory uses an uninsulated butt crimp that is not easy to find in shops. So if your crimp looks like the one in the pic it is probably a factory crimp.

The injector ground wires should all head in the same direction (towards the ECU) and get bundled up with sensor wires and most likely with the timing signal wires from the distributor. The engine loom will get thicker as it heads towards the ECU and picks up more sensor wires along the way.

The injector ground wires connect to transistors inside the ECU. The ECU switches the transistor ON (briefly) to connect the injector ground to the chassis ground and allow current to flow through the injector causing it to fire. Because the injector ground wire is not directly connected to chassis ground, if the battery is connected it is possible for the injector ground to be floating at a potential a few millivolts above chassis ground.

This is not a problem. If the battery is disconnected the reading will go to zero.

Cheers... jondee86

Hi Jondee,

Thank you for confirming the picture is the standard factory tee. I thought it was a bodge job carried out by the previous owner, but this proves it hasn't been messed with - in terms of the ground anyway.

Would the earth on the intake play a part if it wasn't clean? It was connected but didn't inspect how clean it was at the time.

Alex170984 wrote:Would the earth on the intake play a part if it wasn't clean?

A lot of crusty crud or corrosion could cause a problem, but generally speaking, the action of bolting the ring terminal down would be sufficient to break through surface corrosion and make a decent contact. Clean is always better, but a wipe with a rag is usually all that is needed.

Just check that you have zero resistance between the ring connector and the head.

Cheers... jondee86

The reasonable man adapts himself to the world; the unreasonable onepersists in trying to adapt the world to himself. Therefore, all progressdepends on the unreasonable man.

The grounding location on the intake manifold is common for all 4 of the injectors. If its a good ground for 2 injectors, it should be OK for the other 2 injectors. It is must likely a bad plug pin or wire. You are going to have to check each wire run to find the problem.Davew7

when I heard that the clutch safety switch had been tampered with that told me that someone had been into the wiring

when I changed the motor on my 88SC and 89SC I disconnected the harness at the ECU and feed it through the rear firewall and put it on topof the motor (after the rebuild I attached the harness at the block then set it on top then installed the motor then feed the main harness through the rear fire wall)

doing it this way puts less stress on the wire harness

the OP (after I asked) said that this was a engine swapmy 85 MR2 the main wire harness came through the rear fire wall at a different location then the SC wire harness you either have to drill a new fire wall hole or put a lot of stress on the wire harness (IMO) in an effort to try to make it work

its hard to help people when you have to pull information out of them and its one reason I don't help a lot of people

I would put the car back together and get the factory manual and follow the testing procedures found in the factory manual

Alex170984 wrote:Does the head to chassis earth, via the electrical connector actually do anything?

Not sure which ground wire you are referring to, but if the factory put a ground wire from the head to the chassis, it was done for a good reason. Ground wires are provided to ensure that there is a low resistance return path to the battery for every electrical component that runs 12V to ground.

The starter motor draws a heavy current and will have a thick ground wire located close by. The ignition (spark plugs) ground to the head as do the ECU grounds. So the ground wire from the head to the chassis is to make sure that there is a good low resistance ground path from the head rather than relying solely on the starter ground. There will usually also be a ground wire from the gearbox to the chassis.

Fundamentally, the ground wires act as a current return to the battery, much like the waste pipes in a house acts as a drain for the water from sinks, basins and showers. If a pipe gets clogged, the water can't get away, and that is equivalent to a bad (high resistance) ground connection. If the current can't return to the battery by the path of least resistance, it will have to find another path to ground.

Under these circumstances, it is possible for the engine to sit at a potential higher than zero/battery negative voltage. When that happens the ECU, sensors, gauges etc will no longer be seeing full battery voltage. At this point weird sh*t happens

So, the word is... you can never have too many ground connections.

Cheers... jondee86

The reasonable man adapts himself to the world; the unreasonable onepersists in trying to adapt the world to himself. Therefore, all progressdepends on the unreasonable man.

The earth I'm referring to comes off the engine hook on the RHS of the head to a black connector. This then plugs into a wire bolted to the chassis strut tower. This is connected to a wire that bolts to the injector resister bolt on the chassis, sound longer winded than it should be sorry.

I've measured the earth voltage on the head and or inlet manifold with and without this connected and it's 0.04v.

A ground wire (with a connector) that runs from the engine hook bolt to a chassis bolt sounds legit. If it has a ring terminal on each end it will be factory. But there is no reason for the resistor pack to have a ground wire, so I don't know why that would be there ?

At this stage I wouldn't be too concerned about 0.04V between the head/manifold or block and the battery negative with the key ON. Most circuits will have a little bit of voltage drop. Better to wait until you have the engine running and then check for voltage drop. With the key OFF, disconnect the battery positive and check the resistance from the head/manifold/block etc to the negative terminal.

Cheers... jondee86

The reasonable man adapts himself to the world; the unreasonable onepersists in trying to adapt the world to himself. Therefore, all progressdepends on the unreasonable man.

I stripped the wiring back to the ECU plugs for the injector grounds and live and there were no broken wires that were interfering with any live leads. There were a few broken strands on the live side so I cut these back and crimped back together then tested to make sure I still had 12v which I do.

The earth which connects the cylinder head on the engine hook, to the chassis strut tower wasn't doing anything so I've bought a thicker earth strap and connected it to the battery negative and another bolt hole on the cylinder head.

I have cut off no4 injector clip and replaced with a new clip, retested all four injector plugs and I have 12v on all live and 0-0.05v on all grounds. Before I had 0v on 1, 2 & 3 and 12v on no4.

I did cut off the injector clip on 4 before I made the new ground connection and it wasn't showing 12v any longer, so I'm not sure what or how it had 12v as the earth made no difference.

Unfortunately due to having hardly any time I have to do this in drips and drabs and I've made a start on reconnecting the fuel rail and lines. I know I've got to reinstall the intercooler and AFM before I attempt to start the car. I'll do a spark test before I attempt to run the car first to rule out anything else, as stupidly I did not do so before I took it all apart.

It does seem that injector/fuel related woes are common as I've read another thread recently with the guy with his 4AGZE DLI AFM mix -

'the OP (after I asked) said that this was a engine swapmy 85 MR2 the main wire harness came through the rear fire wall at a different location then the SC wire harness you either have to drill a new fire wall hole or put a lot of stress on the wire harness (IMO) in an effort to try to make it work '

Hi Dave,

I've just been re-reading the posts in my thread and come across this bit.

Your 85 AW11 was pre-supercharger, that meant that mine (March 1990) AW11 has different locations of holes in the rear bulkhead where the wires poke through. My best mate also did a conversion on his '86 AW11 and he had problems getting the supercharger unit in, as the chassis is different.

So, there was no effort in making it work, as my car is the same model year as the AW11 supercharger - just thought i'd clear that up.